Field of the Invention
In rail vehicles, in particular of regional transport, waste water tanks are, for example, incorporated at the inner side of the carriage. Such tanks may freeze when they are subjected for a very long period of time (several days) to temperatures substantially below 0° C. if they have previously not been emptied by means of a suction installation. Such situations occur exclusively in winter when, for example, rail vehicles remain on a relatively open railway line with no possibility of recovery or are parked in an unplanned manner without an energy supply.
In contrast to a fresh water tank, for environmental protection reasons it is not permitted to empty the waste water tank onto the track in order to prevent the tank from becoming fractured as a result of the formation of ice with subsequent leakage of the thawing tank and contamination of the vehicle inner space.
For the above reasons, waste water tanks have often been constructed with double walls, which involves increased costs. Alternatively, waste water tanks were also constructed on the outer side, without protection from discharge in the event of leakage. However, tanks which are constructed at the outer side and their fitting construction and the connections thereof are more complex, in particular more costly and heavier than tanks which are fitted at the inner side.
In addition in the prior art, the measure has been taken to detect leakages by means of the increased use of sensors and to separate the tank region by means of barriers. However, this also does not afford the possibility of preventing contamination of the rail vehicle in the event of a relatively large quantity of fluid.